Despite recent advances in our understanding of the development of Myeloproliferative Neoplasms (MPNs), the pathophysiology of these disorders remains poorly understood. Especially the predisposition of MPN patients to transform to acute leukemia is not elucidated. Based on our observation that the transcription factor nuclear factor erythroid 2 (NF-E2) is overexpressed in the majority of MPN patients, we have established a murine model for MPNs, by overexpressing NF-E2 in vivo. Besides the JAK2 V617F and c-MpI W515X mouse models, this is the only murine model of MPN that employs a molecular aberration observed in MPN patients. NF-E2 was overexpressed in all hematopoietic lineages including hematopoietic progenitor cells. Two independently generated founder lines show a phenotype with many features of MPNsj including thrombocytosis, splenomegaly and MPN-like changes in bone marrow (BM) histology. The number of BM erythroid, myeloid and megakaryocytic precursors are significantly increased in NF-E2 transgenic (tg) mice, notably the number of autonomous, EPO-independent erythroid colonies. EPO-independent colonies are a pathognomonic hallmark of MPN patients. NF-E2 transgenic mice display significantly increased mortality with autopsy findings resembling those of MPN patients including splanchnic thrombosis and bleeding diatheses. At 20 months of age, one mouse (7.6%) developed acute leukemia. Our murine model therefore displays a phenotype closely resembling many features of MPN. In addition, our preliminary data indicate that NF-E2 overexpression may predispose to the development of acute leukemia. Based on this data, we formulate the following hypotheses: Hypothesis 1: NF-E2 overexpression alters hematopoietic stem cells (HSCs) resulting in the development of an MPN phenotype. NF-E2 overexpression causes cellautonomous changes in HSCs, the phenotype is therefore transplantable and constitutes a hematopoietic stem cell disorder. Specific Aim 1: To perform primary and secondary transplants and to characterize the stem cell compartment of NF-E2 transgenic donor and recipient mice. Hypothesis 2: NF-E2 overexpression constitutes a pre-leukemic state and predisposes to the evolution to acute leukemia. Specific Aim 2: To treat NF-E2 transgenic and control mice with the mutagen N-ethyl-N-nitrosourea ENU and observe the frequency of leukemic transformation. Hypothesis 3: The pathophysiological changes evoked by NF-E2 overexpression are treatable by pharmacologic intervention. Specific Aim 3: To treat NF-E2 transgenic mice with pharmacological agents currently in pre-clinical or phase I clinical trials for MPN patients.